We herein present a case of cardiac sarcoidosis with atrioventricular (AV) block that was evaluated using magnetic resonance imaging (MRI) before and after pacemaker implantation. An echocardiogram showed wall thinning in the basal septum. MRI showed late gadolinium enhancement in the interventricular septum and right ventricle. Fluorine-18-fluorodeoxyglucose positron emission tomography (PET) demonstrated abnormal uptake in the same area. An MR-conditional pacemaker was implanted to treat AV block. Steroid treatment resulted in the remission of the cardiac lesions and AV block, as confirmed by PET and MRI. MR-conditional pacemakers are thus considered to have great advantages in treating cardiac sarcoidosis with AV block.